Hsp70 proteins, similar to Escherichia coli DnaK, in chloroplasts and mitochondria of Euglena gracilis.

Abstract

The heat-shock response of Euglena gracilis was studied by pulse-labeling cells with [35S]sulfate at both the normal growth temperature (21.degree.C) and an elevated temperature (36.degree.C). Analysis of the labeled proteins by polyacrylamide gel electrophoresis indicated that the rate of synthesis of at least 3 major and 15 minor minor polypeptides increased in cells grown at the higher temperature. Three of the proteins appear to be immunologically related to the ubiquitous .apprxeq. 70-kDa heat-shock protein (Hsp 70) family. One protein of 68 kDa was found in the cytoplasm (P68cyt) and was the major heat-shock protein in Euglena gracilis. Two other proteins, 68 and 70 kDa, were localized in mitochondria (P68mit) and chloroplast (P70chl), respectively, and they crossreacted with a polyclonal antibody raised against the Escherichia coli heat shock protein DnaK. Like DnaK, P68mit and P70chl could be phosphorylated in vitro with [.gamma.-32P]ATP in a reaction that was stimulated by Ca2+. A protein with characteristics similar to those of P70chl was also found in chloroplasts isolated from maize and spinach.